136 Variable Illuminating Power of Coal Gas. 



ARTICLE X. — On the Variable Illuminating Power of Coal 

 Gas; by William E ; A. Aikin, Prof. Chem., &c, Univer- 

 sity of Maryland.* 



(Read before the American Association for the Advancement of Science, 

 at the Baltimore Meeting, May, 1858.) 



In common with a large number of our citizens, my attention 

 was directed some short time since, to a somewhat sudden, inex- 

 plicable and enormous increase in the amount of our quarterly 

 bills for gas consumed ; an increase equal at times to an advance 

 of a hundred per cent over the corresponding quarter of the pre- 

 ceding year. As it would have been absurd to suppose a simul- 

 taneous derangement of all the meters over an extensive district 

 it was obvious that the difficulty could not lie in any error in the 

 registry of the gas, but in its illuminating power, necessarily re- 

 quiring the consumption of a greater bulk of gas to produce a 

 given quantity of light. Feeling curious to know how this 

 difference could have occurred, I set myself to work to ascertain, 

 if possible, what causes could be acting to diminish the illuminat- 

 ing power of the gas. 



It has long been known that the quality of the gas produced 

 from the fat coals is very materially influenced by the circum- 

 stances of the decomposition. In the elaborate experiments made 

 some years ago, on a most extended scale by ileclley, the British 

 Engineer, as detailed in his report to a committee of the House of 

 Commons, we find this subject most satisfactorily discussed. 

 Below a cherry red heat the products obtained by heating coal in 

 close vessels contains hardly any illuminating material. At that 

 temperature it is furnished most freely, but after having been 

 formed is liable to decomposition, involving a loss of carbon by 

 contact with any highly heated surface in passing through the 

 apparatus. Such decarbonization increasing with the degree of 

 heat, with the extension of the red hot surface, and with the time 

 of contact. Again, the duration of heat is most important, the 

 best gas coming over during the first hour, the quality rapidly 

 deteriorating, until at the expiration of four hours the product is 

 worth very little to the consumer, and after five hours may be 

 considered as worthless. But the bulk of such worthless gas that 

 can still be obtained by pushing the process to completion is very 

 considerable, equal sometimes to § of all that passes over. 



* Cited from Silliman's Journal. 



